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Plan 9 - man page for rendezvous (plan9 section 2)

RENDEZVOUS(2)					 System Calls Manual					RENDEZVOUS(2)

NAME
rendezvous - user level process synchronization
SYNOPSIS
#include <u.h> #include <libc.h> ulong rendezvous(ulong tag, ulong value)
DESCRIPTION
The rendezvous system call allows two processes to synchronize and exchange a value. In conjunction with the shared memory system calls (see segattach(2) and fork(2)), it enables parallel programs to control their scheduling. Two processes wishing to synchronize call rendezvous with a common tag, typically an address in memory they share. One process will arrive at the rendezvous first; it suspends execution until a second arrives. When a second process meets the rendezvous the value arguments are exchanged between the processes and returned as the result of the respective rendezvous system calls. Both processes are awakened when the rendezvous suc- ceeds. The tag space is common to processes in the same file name space, so rendezvous only works between processes in the same file name space. If a rendezvous is interrupted the return value is ~0, so that value should not be used in normal communica- tion.
SOURCE
/sys/src/libc/9syscall
SEE ALSO
segattach(2), fork(2)
DIAGNOSTICS
Sets errstr.
BUGS
The correlation of rendezvous tags and file name space is a historical accident. If two unrelated processes happen to be in the same name space and do a rendezvous, trouble will result. The solution is to call rfork(RFNAMEG) (see fork(2)) in programs that use rendezvous unless they need to share the name space with their parent. This is especially important in Alef programs. RENDEZVOUS(2)


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